Ion implantation has been used in the semiconductor and other industries for many decades to modify the composition of substrate material. In particular, beam-line and cluster beam ion implantation systems are widely used today in the semiconductor industry. Beam-line and cluster beam ion implantation systems accelerate ions with an electric field and then select ions with the desired mass-to-charge ratio. The selected ions are then implanted into the substrate, thereby doping the substrate with the desired dopant material. These systems have excellent process control, excellent run-to-run uniformity, and provide highly uniform doping across the entire surface of state-of-the art semiconductor substrates.
Recently, plasma doping has been used to dope substrates. Plasma doping is sometimes referred to as PLAD or plasma immersion ion implantation (PIII). Plasma doping systems have been developed to meet the doping requirements of state-of-the-art electronic and optical devices. Plasma doping systems are fundamentally different from conventional beam-line and cluster beam ion implantation systems. Plasma doping systems immerse the substrate in a plasma containing dopant ions and then bias the substrate with a series of negative voltage pulses. The negative bias on the substrate repels electrons from the surface of the substrate, thereby creating a sheath of positive ions. The electric field within the plasma sheath accelerates ions toward the substrate, thereby implanting the ions into the surface of the substrate.